Method and system for measuring local ultraviolet exposure

ABSTRACT

One variation of a method for measuring ambient ultraviolet light radiation including: calculating a target direct orientation of a light exposure device based on a location, a current date and time, and a direct solar position model; calculating a target diffuse orientation of the light exposure device based on the location, the current date and time, and a diffuse solar position model; in response to detecting alignment between orientation of the light exposure device and the target direct orientation, recording a direct ultraviolet value; in response to detecting alignment between orientation of the light exposure device and the target diffuse orientation, recording a diffuse ultraviolet value; in response to detecting alignment between orientation of the light exposure device and a target global orientation, recording a global ultraviolet value; and calculating an ultraviolet index based on the global ultraviolet value, the direct ultraviolet value, and the diffuse ultraviolet value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation application of U.S. patentapplication Ser. No. 15/648,158, filed on 12 Jul. 2017, which claims thebenefit of U.S. Provisional Application No. 62/434,184, filed on 14 Dec.2016 and U.S. Provisional Application No. 62/404,131, filed on 4 Oct.2016 and U.S. Provisional Application No. 62/361,414, filed on 12 Jul.2016, and U.S. Provisional Application No. 62/380,455, filed on 28 Aug.2016, each of which is incorporated in its entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the field of measuring ultravioletlight radiation and more specifically to a new and useful method forlocally measuring ultraviolet radiation through an ultraviolet radiationmeasurement device.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B are flowchart representations of a first method;

FIG. 2 is a flowchart representation of the first method;

FIG. 3 is a flowchart representation of the first method; and

FIGS. 4A and 4B are schematic representations of the first method; and

FIG. 5 is a schematic representation of the first method.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. First Method

As shown in FIGS. 1-5, a method S100 includes accessing a location of alight exposure device including an ultraviolet sensor in Blocks S112 andS114; calculating a target direct orientation of the light exposuredevice based on the first location, a current date and time, and adirect solar position model, the ultraviolet sensor approximately normalthe Sun when the light exposure device occupies the target directorientation at approximately the current time in Block S122; calculatinga target diffuse orientation of the light exposure device based on thefirst location, the current time, and a diffuse solar position model,the ultraviolet sensor biased away from the Sun and above the horizonwhen the light exposure device occupies the target diffuse orientationat approximately the current time in Block S124; tracking an orientationof the light exposure device in Block S130; in response to detectingalignment between orientation of the light exposure device and thetarget direct orientation at approximately the current time, recording adirect ultraviolet value read from the ultraviolet sensor in Block S142;in response to detecting alignment between orientation of the lightexposure device and the target diffuse orientation at approximately thecurrent time, recording a diffuse ultraviolet value read from theultraviolet sensor in Block S144; in response to detecting alignmentbetween orientation of the light exposure device and a target globalorientation at approximately the current time, recording a globalultraviolet value read from the ultraviolet sensor in Block S146; andcalculating a current ultraviolet index at the light exposure devicebased on the global ultraviolet value in Block S150.

One variation of the method S100 shown in FIG. 1B includes: accessing afirst location of a light exposure device including an ultravioletsensor; tracking an orientation of the light exposure device; inresponse to detecting alignment between orientation of the lightexposure device and a target global orientation window at a first time,recording a first value read from the ultraviolet sensor as a globalultraviolet value; and calculating a first ultraviolet index at thelight exposure device corresponding to the first time based on theglobal ultraviolet value.

2. Applications

Generally, the method S100 can be executed by a light exposure deviceand a software program executing on a mobile computing device toaccurately monitor a user's ultraviolet exposure over time by: defininga target orientation of the light exposure device in real space thatlocates an ultraviolet sensor in the light exposure device at a knownangular offset from the Sun based on an approximate geolocation of thelight exposure device and a current date and time; opportunisticallyrecording ultraviolet values through the ultraviolet sensor when thelight exposure device is aligned to this target orientation during asampling interval; matching these ultraviolet values to one of a set ofpredefined ultraviolet exposure models for this sampling interval;integrating the ultraviolet exposure model over the duration of thesampling interval to accurately estimate the user's ultraviolet exposureduring this sampling interval; and repeating this process over time(e.g., over the course of one day) and summing ultraviolet exposuresduring each sampling interval over this period of time to calculate theuser's total ultraviolet exposure during this period of time period oftime while also achieving a minimal sampling rate, reducing powerconsumption, and extending battery life of the light exposure deviceduring this period of time. In particular, during a sampling interval,the light exposure device can: record multiple ultraviolet values atdiscrete orientations of the light exposure device relative to the Sunand/or relative to the Earth; process (e.g., “fuse”) these ultravioletvalues and orientations of the light exposure device at times that theseultraviolet values were recorded into an estimate of a currentultraviolet index at this time; and predict ultraviolet indices local tothe user will be exposed over a subsequent duration of time (e.g.,fifteen minutes) by selecting a particular predefined ultraviolet indexmodel (e.g., a “UV curve”)—from a set of predefined ultraviolet indexmodels—that best aligned to the current ultraviolet index estimate.Therefore, the light exposure device can opportunistically record alimited number of ultraviolet values over an extended duration of time(e.g., fifteen minutes) to accurately estimate an ultraviolet index towhich a user is exposed during this duration of time. The light exposuredevice (or a native application or other software program executing onan affiliated mobile computing device) can then integrate theseestimated ultraviolet indices—including values generated directly fromultraviolet values read from the ultraviolet sensor in the lightexposure device and estimated from predefined ultraviolet indexmodels—over time to accurately estimate the user's total ultravioletexposure.

Thus, the method S100 can be implemented to both track and anticipate anultraviolet exposure for a user proximal the light exposure device overan exposure period. Based on the ultraviolet exposure, the lightexposure device can recommend behavioral modifications to protect a userassociated with (e.g., wearing) the light exposure device from sundamage. For example, the light exposure device and/or the softwareprogram can prompt a user to reapply sunscreen or move to a shaded areaout of direct Sunlight. Thus, the method S100 can function: toopportunistically collect ultraviolet exposure data, thereby reducing oreliminating a need for a user to perform manual readings; tointermittently record data through sensors in the device and to projectultraviolet exposure over extended durations of time based on theseintermittent data, thereby extending battery life of the light exposuredevice; and to accurately estimate the user's exposure to ultravioletradiation over time based on these data such that prompts to increasesun exposure, decrease sun exposure, or apply sunscreen, etc. served tothe user according to these ultraviolet exposure data are accurate andrelevant to the user.

In one application shown in FIG. 1A, Blocks of the method S100 can beimplemented by a light exposure device, such as a wearable device orother portable device with an integrated ultraviolet sensor that a usermay carry. For example, the light exposure device can be a smartphone; aGPS-enabled smartwatch; an ultraviolet-sensitive band configured to beworn on a user's wrist; a ring worn on a finger; a pin, button, broochconfigured to be clipped or attached to an item of clothing or to a bag;a drink cooler; a beach umbrella; a ski pole; a golf bag; and/or anyother portable or mobile device that a user may carry in order to trackthe user's corporeal ultraviolet exposure over a period of time (e.g.,per day). The light exposure device can also be linked to and cancooperate with a mobile computing device (e.g., a mobile phone, atablet, a smartwatch, etc.) to implement Blocks of the method S100.

Thus, the method S100 can be implemented by a light exposure deviceand/or a mobile computing device to track ultraviolet exposure (e.g.,UVB radiation exclusively or UVA, UVB, and UVC) and recommend behaviormodifications to limit erythemal impact, skin damage, etc. to a userwearing or otherwise interfacing with the light exposure device.

2.1 Applications: Accuracy

Based on the location of the mobile computing device and a current dateand time, the light exposure device can implement Blocks of the methodS100 to estimate a solar position of the Sun relative the light exposuredevice based on a local copy of a derived solar position model stored onthe light exposure device. From this solar position, the light exposuredevice can calculate target orientations of the light exposure devicerelative to the Earth to record a limited number of ultraviolet valuesfrom which the light exposure device can accurately estimate the currentultraviolet index proximal the user. In particular, the method S100 canbe implemented by the light exposure device: to calculate a solarposition of the Sun in relation to a location near the light exposuredevice; based on the solar position, to define target orientations forrecording ultraviolet values with the light exposure device when anultraviolet sensor in the light exposure device is aligned with the Sun(i.e., a target “direct” orientation), at an angle offset and biasedfrom the Sun toward open sky (i.e., a target “diffuse” orientation),and/or normal to the Earth's surface (i.e., a target “global”orientation directed toward the user's zenith); to arm a controllerintegrated into the light exposure device to record ultraviolet valuesthrough the ultraviolet sensor; and to record ultraviolet values throughthe ultraviolet sensor in response to non-specific motion of the lightexposure device resulting in alignment of the light exposure device tothese target orientations, such as within a preset tolerance ororientation window.

By consistently recording multiple redundant ultraviolet valuesaccording to a predefined orientation schedule (e.g., direct and diffuseorientations relative to the Sun and a global orientation relative toEarth) per sampling interval, the light exposure device can: calculate asingle ultraviolet index based on the global ultraviolet value; and/orfuse multiple ultraviolet values (e.g., the direct and diffuseultraviolet values) read when the light exposure device occupied thesetarget orientations during a sampling interval into a single ultravioletindex value that represents a relatively accurate measure of the user'sultraviolet irradiance during this sampling interval. Furthermore, bynarrowing the target orientation range for recording ultraviolet valuesin the global, direct, and/or diffuse orientations as opportunisticultraviolet values are recorded during the sampling interval, the methodS100 can collect more accurate ultraviolet values and reduce error in anultraviolet index derived from these ultraviolet values.

The method S100 can also be implemented to calculate an “instant”ultraviolet index at the light exposure device and to track ultravioletexposure immediately surrounding the light exposure device—as opposed toapproximating a local ultraviolet index based on an ultravioletradiation reading recorded remotely from the light exposure device(e.g., at a weather station)—as the light exposure device traverses atrajectory intersecting current target direct, diffuse, and globalorientation windows over a period of time. In particular, the methodS100 can be implemented to accurately track ultraviolet exposure along atrajectory traversed by the light exposure device over a samplinginterval by intermittently recording ultraviolet values detected by theultraviolet sensor integrated into the light exposure device. Thus, thelight exposure device can implement Blocks of the method S100 to improveaccuracy of real-time location-based ultraviolet radiation measurements.

For example, a mobile computing device linked to the light exposuredevice can determine that it is located in San Francisco, Calif., whichencompasses a multitude of varying microclimates within forty-ninesquare miles. When the light exposure device wirelessly connects to themobile computing device over short-range wireless communicationprotocol, over a local wireless network, or over a wired connection, themobile computing device can upload its location to the light exposuredevice. In this example, a user wearing the light exposure device maytravel from the Marina neighborhood of San Francisco to the South ofMarket (i.e., “SoMa”) neighborhood and then to the Potrero Hillneighborhood on a particular day. A global ultraviolet value can berecorded by a single static weather station in the North Beachneighborhood, and an approximate ultraviolet index for San Francisco atthis time can be calculated based on this single ultraviolet value.However, on this day, weather in the North Beach neighborhood may becool and foggy while weather in the Marina neighborhood may be warmerand slightly overcast, weather in the “SoMa” neighborhood may be windyand clear, and weather in the Potrero Hill area may be warm and sunny.While the ultraviolet index calculated based on the single ultravioletvalue recorded by the weather station may be approximately correct forthe North Beach neighborhood, this ultraviolet index may be highlyinaccurate (e.g., under-representative) for these other neighborhoods ofSan Francisco.

However, in this example, the light exposure device can implement Blocksof the method S100 to track and record instant ultraviolet valuescoincident with the light exposure device and the user wearing the lightexposure device throughout this day. In particular, an ultravioletsensor integrated into the light exposure device can record ultravioletvalues intermittently throughout this day; and the light exposure devicecan manipulate these data to track the user's cumulative ultravioletexposure throughout this day and as conditions change.

Therefore, the light exposure device can implement Blocks of method S100to account for local variations in ultraviolet radiation indices—such aswhen the light exposure device is located in a shaded area, indoors, orunder local cloud cover—in calculating cumulative ultraviolet exposureover a sampling interval. For example, outdoors (e.g., on a roof of abuilding) at a particular geolocation, the light exposure device canrecord ultraviolet values and, from the ultraviolet values, calculate anultraviolet index of 6.0 for the particular geolocation. However,indoors (e.g., inside the building) at the particular geolocation, thelight exposure device can record lower ultraviolet values and, from theultraviolet values (e.g., the global ultraviolet value), calculate anultraviolet index of 0.1 for the particular geolocation.

In order to track ultraviolet exposure as the light exposure devicemoves along a trajectory, the mobile computing device can intermittently(e.g., every hour, day, or week) transmit location information to thelight exposure device when the light exposure device and the mobilecomputing device remain within a threshold area rather than continuouslymonitoring a path of the light exposure device and the mobile computingdevice. The light exposure device can implement a geolocation (e.g., aGPS location) received from the mobile computing device to calculate anapproximate solar position (i.e., a position of the Sun) relative to thelight exposure device and to calculate target orientations of the lightexposure device at which the light exposure device is to recordultraviolet values that are then fused to calculate an accurate estimateof the ultraviolet index local to the light exposure device. Inparticular, the light exposure device can pass the approximate locationof the light exposure device, the current date, and the current timeinto direct, diffuse, and global solar position models to calculatethese target orientations, which may be accurate to within a thresholdtolerance tighter than an accuracy of orientation or position sensors inthe light exposure device.

The light exposure device can, thus, implement a singular geolocationover a geographic area (e.g., a 10 mile radius) in which the mobilecomputing device is located to calculate the target direct, diffuse, andglobal orientations, thereby leveraging accuracy of the solar positionmodels and compensating for relative inaccuracy of the orientationand/or position sensor in the light exposure device. Furthermore, themobile computing device can send a geolocation update to the lightexposure device (exclusively) when the mobile computing device movesoutside of this geographic area and the light exposure device is nearby(e.g., within wireless range of the mobile computing device).

Thus, the light exposure device can implement Blocks of the method S100in real-time to accurately and promptly alert a user of her currentultraviolet exposure and/or risk of sunburn. By recording high qualityultraviolet values, the light exposure device can accurately calculateultraviolet exposure to prevent transmission of asynchronous andirrelevant notifications to a user. For example, on a sunny day, a usermay experience ultraviolet exposure so great that the user's skin mayburn within minutes (e.g. five minutes) of moving outdoors. Thus, thelight exposure device (and/or the mobile computing device) can transmita timely notification to the user to move indoors, apply sunscreen,and/or otherwise avoid continued ultraviolet exposure. However, if thelight exposure device were to calculate the current ultraviolet indexand/or project ultraviolet exposure inaccurately, the light exposuredevice can alert the user of excessive exposure after the user may havealready been subjected to excessive ultraviolet exposure. On a cloudyday, a user may avoid excessive ultraviolet exposure outdoors overseveral hours (e.g., four hours). Thus, if the light exposure devicewere to calculate the current ultraviolet index and/or projectultraviolet exposure inaccurately, the light exposure device canneedlessly alert the user of excessive exposure well before the user mayexperience sunburn from excessive ultraviolet exposure. Thus, the lightexposure device can execute the method S100 to promptly warn a user ofrisk of sunburn while avoiding irritating the user with superfluousalerts.

2.2 Applications: Opportunistic Readings

The method S100 can also be implemented to opportunistically recordultraviolet values when conditions defined by the light exposure deviceare met, such as when inadvertent movement of the light exposure deviceby the user aligns its integrated ultraviolet sensor to precalculateddirect, diffuse, and global orientations, thereby reducing oreliminating a need for the user to manually and intentionally orient thelight exposure device in preparation for such readings, which mayotherwise frustrate the user, limit use of the light exposure deviceover time, and reduce accuracy of the user's ultraviolet exposurecalculated by the light exposure device over time due to lowrepeatability and high degrees of error in manual in positioning of thelight exposure device by a user.

In one implementation, orientation sensors (e.g., a multi-axisgyroscope, compass, accelerometer, and/or tilt sensor) integrated intothe light exposure device can output yaw, pitch, and roll orientationsof the light exposure device, such as relative to the reference frame ofthe Earth or relative to an arbitrarily-defined reference frame. Forexample, the light exposure device can include a compass sensor, amulti-axis tilt sensor or accelerometer, and a multi-axis gyroscopicsensor; and the light exposure device can fuse an absolute compassdirection output by the compass, angular velocity values output by thegyroscopic sensor, and acceleration values output by the tilt sensor oraccelerometer into a pitch, yaw, and roll position of the light exposuredevice relative an Earth reference frame per sampling interval. From thesolar position, the light exposure device can define a target directorientation for the light exposure device, such that, when outputs ofthese sensors indicate that the light exposure device is aligned withthe target direct orientation, an ultraviolet sensor integrated into thelight exposure device is directed orthogonal the Sun.

In particular, rather than prompting a user wearing (or carrying) thelight exposure device to manually align the light exposure device withthe target direct orientation during a sampling interval, the lightexposure device can: intermittently wake from a sleep state to collectultraviolet data (e.g., once per fifteen-minute interval); define targetdirect, diffuse, and/or global orientations for collection ofultraviolet values during this interval; regularly sample theorientation sensors during this interval to monitor the orientation ofthe light exposure device; automatically record ultraviolet values fromthe ultraviolet sensor in response to the orientation of the lightexposure device falling within a threshold difference from each of thetarget direct orientation, the target diffuse orientation, and/or theglobal orientation; transform these ultraviolet values into aultraviolet radiation exposure value for the user for this interval; andthen return to the sleep state. The light exposure device can repeatthis cycle over time, such as during known daylight hours for thecurrent date and location of the light exposure device, and aggregateultraviolet radiation exposure values for each interval during a singleday into a cumulative ultraviolet radiation exposure value for the userfor this day.

For example, the user may rotate the light exposure device into thetarget global orientation while opening a door or performing any othertask; in response to detecting that its orientation has fallen within athreshold difference of the target direct orientation (or a range ofdirect orientations) for the current time of day, date, and approximategeolocation of the light exposure device, the light exposure device canrecord a global ultraviolet value. The light exposure device cansimilarly record ultraviolet values when the detected orientation of thelight exposure device falls within threshold differences of the targetdirect and diffuse orientations. (However, the light exposure device canopportunistically collect ultraviolet data for other target orientationsof the light exposure device based on predicted positions of the Sunrelative to Earth at corresponding times of day, days of the year, andlocations stored on the light exposure device.)

As shown in FIG. 2, the light exposure device can also include anambient light sensor configured to output a signal corresponding to alevel of incident ambient (visible) light and arranged proximal theultraviolet sensor in the light exposure device. For example, inresponse to lack of a signal from the ambient light sensor during knowndaylight hours at the current time and location of the light exposuredevice, the light exposure device can determine that the ambient lightsensor is obscured, such as by a sleeve covering a wrist on which thelight exposure device is worn by a user. Because the ambient lightsensor is adjacent the ultraviolet sensor, obfuscation of the ambientlight sensor may indicate similar obstruction of the ultraviolet sensor.Therefore, the light exposure device can postpone or cancel collectionof ultraviolet data during a current sampling interval while the ambientlight sensor is obstructed, thereby avoiding recordation of aberrant orirrelevant ultraviolet values when conditions surrounding theultraviolet sensor are unfavorable to collection of accurate sensordata.

In the foregoing example, the light exposure device can also detectpresence of ambient light based on an output of the ambient lightsensor, confirm that the ambient light and ultraviolet sensors are notobscured, and then enable collection of ultraviolet data through theultraviolet sensor. (Similarly, the light exposure device canconcurrently sample the ambient light sensor and the ultraviolet sensorwhen the light exposure device aligns with a target orientation and thenretroactively confirm that the ultraviolet sensor was not obscuredduring this sampling interval based on an ambient light level read fromthe ambient light sensor during this same sampling interval.) However,in response to detecting the presence of ambient light but little or noultraviolet radiation (e.g., UVB specifically, which may penetrate fusedsilica and fused quartz but may not penetrate other common glasses), thelight exposure device can determine that it is located indoors andestimate the user's ultraviolet radiation exposure at null until anincrease in detected incident ultraviolet radiation—indicating that thelight exposure device is outdoors—is recorded.

Furthermore, the ambient light sensor can cooperate with the ultravioletsensor to prioritize target orientations for recording ultravioletvalues. For example, in response to detecting the presence of ambientlight, the light exposure device can record a direct ultraviolet valuein response to detecting its alignment with the target directorientation, a diffuse ultraviolet value in response to detecting itsalignment with the target diffuse orientation, and a global ultravioletvalue in response to detecting its alignment with the target globalorientation. In this example, the light exposure device can determinethat the direct ultraviolet value corresponds to an ultraviolet indexsignificantly less than ultraviolet indices corresponding to the globaland diffuse ultraviolet values. Thus, the light exposure device candetermine that its location is outside yet away from direct sunlight,such as in a shaded area or under overcast skies, and can temporarilyreject direct ultraviolet values recorded by the ultraviolet sensor,thereby applying the direct and diffuse ultraviolet values to calculatea current ultraviolet index based on shade or cloudy sky sun exposuremodels and algorithms.

2.3 Applications: Efficiency & Resource Conservation

Additionally, the light exposure device can implement Blocks of themethod S100 to limit processing load and energy consumption by:intermittently recording targeted ultraviolet values once per discretesampling interval (e.g., once per fifteen-minute or one-hour interval);processing global, direct, and/or diffuse ultraviolet values read duringa sampling interval to determine an ultraviolet index at the location ofthe light exposure device at one instance in this sampling interval;selecting a particular, predefined ultraviolet index model—from a set ofsuch ultraviolet index models—based on this calculated ultravioletindex; and implementing this one ultraviolet index model to anticipateultraviolet indices around the light exposure device during theremainder of the sampling interval and until a next set of global,direct, and/or diffuse ultraviolet values read are recorded during anext sampling interval.

Generally, the light exposure device can implement Blocks of the methodS100 to conserve energy by avoiding continuous sampling of theultraviolet sensor and instead: intermittently, opportunistically, andactively recording ultraviolet values at target orientations at discretesampling intervals; selecting a relevant ultraviolet index model (e.g.,an ultraviolet index curve) with an implicit modeling error less thanmeasurement error of orientation and position sensors of the lightexposure device based on ultraviolet values recorded by the lightexposure device during a sampling interval; and then passivelyimplementing this ultraviolet index model to predict the user'sultraviolet radiation exposure until a next sampling interval. In thisnext sampling interval, the light exposure device can again record a newset of ultraviolet values, select the same or other most appropriateultraviolet index model based on these new ultraviolet values, and theimplement this new ultraviolet index model to project the user'sultraviolet radiation exposure during the next sampling interval.

Thus, the light exposure device can be configured to track the user'sultraviolet radiation exposure over a long period of time (e.g., oneweek or one month) without necessitating that its battery be recharged,thereby minimizing dependence on a user to charge the light exposuredevice over time. Nevertheless, by implementing the method S100, thelight exposure device can collect accurate ultraviolet data andtransform these data into accurate estimations of a user's cumulativeultraviolet radiation exposure over a period of time (e.g., one day, oneweek).

However, Blocks of the method S100 can be implemented in any other wayand by any other discrete light exposure device, wearable device, ormobile computing device, etc. to calculate a highly accurate estimationof a user's cumulative ultraviolet exposure while reducing processingpower, extending battery life, and limiting or eliminating manualinvolvement of the user.

3. System

As shown in FIGS. 1A, 1B, and 5, Blocks S112 and S114 of the method S100are described herein as executed by a mobile computing device, such as amobile phone, a wearable computing device (e.g., a “smartwatch”), atablet, a desktop or laptop computer, or any other suitable computersystem equipped to access and transmit location data to the lightexposure device. For example, the mobile computing device can: include aGPS receiver and/or any other geospatial location module configured toidentify a geolocation of the mobile computing device; and a short-rangewireless communication module configured to establish a local wirelessconnection with the light exposure device.

Blocks S122-S150 of the method S100 can be executed by a light exposuredevice, such as a wearable computing device, a smartphone, anultraviolet-sensitive band; a pin, button, and/or brooch; smart glasswear; a smart ring; and/or any other portable computing deviceconfigured to record ultraviolet values.

The mobile computing device can interface and cooperate with a lightexposure device to execute Blocks of the method S100. In oneimplementation, the mobile computing device can transmit location datato the light exposure device, such as over a wireless network or localarea network. Thus, the mobile computing device and the light exposuredevice can include wireless communications modules configured to sendand receive data.

Alternatively, the light exposure device can be integrated into themobile computing device, such that the light exposure device includes aGPS receiver and/or any other location-detecting module configured toidentify a geolocation of the mobile computing device. For example, thelight exposure device can be a GPS-enabled smartwatch worn by a user. Inthis example, the light exposure device can access its location withoutassistance from or wireless communication with a secondary mobilecomputing device.

In one implementation, the light exposure device includes: a housing,such as a plastic injection-molded and thermoplastic elastomer (TPE)over-molded housing; an ultraviolet sensor, such as a digitalultraviolet (UV) index photodiode light sensor or other opticalultraviolet sensor, adjacent a UV-transparent region of an outer surfaceof the housing; memory arranged in the housing; a controller arranged inthe housing and configured to sample the ultraviolet sensor and othersensors housed within the light exposure device and to store incidentsolar radiation data to memory; a wireless communication module arrangedin the housing and configured to receive location data from a localmobile computing device and transmit solar radiation data to a localmobile computing device, such as in real-time, intermittently (e.g., oneper three-minute interval), or asynchronously (e.g., after establishinga wireless connection between the mobile computing device and the lightexposure device); and a rechargeable battery arranged in the housingconfigured to power the controller, sensors, and the wirelesscommunication model.

3.1 Sensors: Orientation and Motion

The light exposure device can include motion and orientation sensorsconfigured to record pitch, yaw, and roll orientations of the lightexposure device, such as relative to the reference frame of the Earth orto an arbitrarily-defined reference frame. Thus, the light exposuredevice can also include an accelerometer or tilt sensor configured todetect pitch and roll orientations of the light exposure device; acompass sensor (e.g., a compass sensor) configured to detect yaworientation of the light exposure device; and a gyro sensor or angularvelocity sensor configured to detect a rate of angular pitch, roll, andyaw motion. In one implementation, the controller can thus transitionfrom an inactive (e.g., “sleep” or “hibernate”) low power mode to anactive mode responsive to an output of the motion sensor and/or predictan activity of the user wearing the exposure-tracking module based on amagnitude and/or frequency of outputs of the motion and orientationsensors.

3.2 Ultraviolet Sensor

The light exposure device also includes an ultraviolet sensor configuredto output a signal proportional to incident ultraviolet radiation. Inone example, the ultraviolet sensor is broadly sensitive to ultravioletradiation and includes an ultraviolet filter configured to passultraviolet radiation within a limited erythemal action spectrum and toreject ultraviolet light outside of this spectrum. The ultravioletsensor can thus define an erythemally-filtered ultraviolet sensor. Inthis example, the ultraviolet filter can pass UVB (which may not passthrough glass) but reject UVA (which may pass through glass); thus whenthe light exposure device detects ambient light at the ambient lightsensor but no ultraviolet radiation at the ultraviolet sensor, the lightexposure device can determine that it is occupying an indoor space.However, because UVA exposure may be proportional to UVB exposure whenoutdoors, the light exposure device can predict both UVA and UVBexposure of a user based on degree of UVB radiation detected at theultraviolet sensor.

In this foregoing example, the filter can also be polarized in order toselectively pass ultraviolet radiation within a narrow range of incidentangles (e.g., normal to the ultraviolet sensor ±5°) in order to increasesensitivity of a signal output by the ultraviolet sensor to itsorientation. The ultraviolet sensor can additionally or alternativelyinclude a diffuser that functions to accommodate angular misalignment ofthe light exposure device from a target orientation by funnelingultraviolet radiation over a wider angular window into a sensing elementin the ultraviolet sensor.

However, the light exposure device can include any other type and/orquantity of ultraviolet sensor.

3.3 Ambient Light Sensor

Additionally, as shown in FIG. 2, the light exposure device can includean ambient light sensor, such as a photodiode, photodetector,phototransistor, or any other optical sensor configured to detect thepresence and/or absence of light. The light exposure device can bearranged within the housing of the light exposure device adjacent anoptically transparent screen or an optically translucent diffuser screenintegrated into an outer surface of the housing. The diffuser screen canbe configured to scatter incident ambient light to yield an effectiveoptical “averaging” effect on incoming light sources.

As described below, the controller can transition from an inactive(e.g., “sleep” or “hibernate” or “low power”) mode to an active mode andcan transition sensors within the light exposure device from inactive toactive, responsive to an output of the ambient light sensor indicatingpresence of light proximal the light exposure device. Likewise, thecontroller can transition from an active mode to an inactive mode andcan transition sensors within the light exposure device from active toinactive, responsive to an output of the ambient light sensor indicatingabsence of light proximal the light exposure device.

3.4 Additional Sensors

Additionally or alternatively, the light exposure device can includeadditional sensors, such as an ambient temperature sensor, a humiditysensor, a heart-rate monitoring sensor, a skin temperature sensor, aninfrared (IR) irradiance sensor, a visible light irradiance sensor, analtimeter, a barometer, a moisture or water exposure sensor, any otherambient condition sensor configured to record parameters of ambientconditions surrounding the light exposure device, and/or any otherbiometric sensor configured to record biometric parameters of a userassociated with the light exposure device.

4. Location

Blocks S112 and S114 of method S100 recite accessing a location of thelight exposure device. Generally, in Blocks S112 and S114, the mobilecomputing device can access a geolocation of the mobile computingdevice, such as through a global positioning system (i.e., “GPS”)receiver integrated into the mobile computing device, and distribute thegeolocation of the mobile computing device to the light exposure device,such as through the wireless communication portal and over a wirelesscommunication network between the mobile computing device and the lightexposure device. The mobile computing device can be configured totransmit location data to the light exposure device in real-time,intermittently (e.g., one per three-minute interval), and/orasynchronously (e.g., after establishing a wireless connection betweenthe mobile computing device and the light exposure device).

If the light exposure device remains within an effectively-small localgeolocation area (e.g., relative to azimuth and zenith angles of theapparent position of the Sun in the sky, or approximately a thirty-mileradius), the mobile computing device can disable transmission of thelocation to the light exposure device. For example, at a first time, themobile computing device can access a GPS location of the mobilecomputing device indicating the mobile computing device is in SanFrancisco and transmit the GPS location to the light exposure deviceover a wireless connection between the mobile computing device and thelight exposure device. In this example, for a week succeeding the firsttime, the light exposure device and mobile computing device travelaround San Francisco but remain within the city limit of San Francisco.During the week, the mobile computing device can disable transmission ofthe GPS location of the mobile computing device. Thus, the lightexposure device can apply a general location of the light exposuredevice (i.e., San Francisco) to a solar position model to calculate theapproximate solar position for discrete times of day in and around SanFrancisco. However, one week after the geolocation event, the mobilecomputing device can detect, through a GPS module, relocation of themobile computing device to San Jose, approximately fifty miles south ofSan Francisco. In response to relocation of the mobile computing deviceoutside of San Francisco, the mobile computing device can transmit anupdated location (i.e., a GPS location within San Jose) to the lightexposure device. Thus, after relocation of the mobile computing deviceand the light exposure device to San Jose, the light exposure device canapply this new location of the light exposure device (i.e., San Jose) toa solar position model to calculate the solar position for discretetimes of day in and around San Jose. Furthermore, by intermittentlytransmitting GPS locations from the mobile computing device to the lightexposure device, the mobile computing device and the light exposuredevice can limit wireless connectivity therebetween, which may limitpower consumption and extend battery life at the light exposure device.Therefore, a user may carry the light exposure device without carryingthe mobile computing device alongside the light exposure device whilestill recording accurate and relevant ultraviolet values.

In another example, the mobile computing device can transmit a locationof the mobile computing device indicating it is currently located inBoulder, Colo. From this location and the current calendar date thelight exposure device can estimate a solar position at 10:42 AM on 21Jul. 2017 in Boulder, Colo. which includes a solar azimuth component(i.e., an angle, in a plane defined by a horizon at a particularlocation, defined between a vector directed toward the Sun and truenorth) of 111.35 degrees, a solar elevation component (i.e., an angledefined perpendicular the horizon and between the horizon and the vectordirected toward the Sun) of 53.39 degrees, a solar declination componentof 20.48 degrees, and a cosine of a solar zenith of 0.8027.

In one implementation, the mobile computing device can track thelocation of the mobile computing device and can intermittently transmita new location to the light exposure device in response to detectingrelocation of the mobile computing device more than a threshold distance(e.g., more than thirty miles). In particular, relocation of the lightexposure device 70 miles from its last stored location may yield adifference of approximately 1° in the zenith for a target directorientation calculated by the light exposure device in Block S122.Similarly, the disk of the Sun subtends approximately 0.5°; the targetdirect orientation calculated by the light exposure device in Block S122and defining intended alignment between the ultraviolet sensor in thelight exposure device and the center of the Sun may instead place theedge of the sun in the center of the field of view of the ultravioletsensor when the light exposure device is oriented in this target directorientation if the light exposure device is offset from its last storedlocation by approximately seventeen miles. Thus, the mobile computingdevice can function to update location data implemented by the lightexposure device to calculate an approximate solar position. Within athreshold distance or area (e.g. forty square miles), the light exposuredevice can approximate a solar position of the Sun that will besubstantially uniform, for a given date and time. However, outside thethreshold distance or area, the light exposure device can calculate anerror due to consistent offset of the approximate solar positioncalculated by the light exposure device and an actual solar positiondetected by ultraviolet values recorded by the ultraviolet sensor and byambient light sensor values recorded by the ambient light sensor. Thus,in response to relocation of the mobile computing device outside of thethreshold distance or range, the mobile computing device can updatelocation information applied by the light exposure device to calculatethe solar position.

Additionally, the mobile computing device can transmit a current timerecorded at the mobile computing device to the light exposure device. Inone implementation, the light exposure device can include an integratedclock or timing device. In response to establishment of a connectionbetween the light exposure device and the mobile computing device, themobile computing device can synchronize the integrated clock of thelight exposure device with a current time recorded at the mobilecomputing device. In this implementation, the mobile computing devicecan intermittently update a current time (e.g., current UTC time) at thelight exposure device in order to improve accuracy of solar positioncalculations executed by the controller of the light exposure devicebased on current time and current location of the light exposure device.

Alternatively, the light exposure device can access a current locationof the light exposure device entered (e.g., manually) by a user into themobile computing device and/or the light exposure device. For example,the user may input an instant zip code, city and state, longitude andlatitude, etc. into the mobile computing device and/or the lightexposure device. The light exposure device can also access its currentlocation from other external devices, such as a cellular tower, Wi-Fihub, or local wireless network, etc.

4. Target Orientations

Block S122 and S124 of the method S100 recite calculating a targetdirect orientation of the light exposure device based on the firstlocation, a current time and current date, and a direct solar positionmodel, the ultraviolet sensor approximately normal the Sun when thelight exposure device occupies the target direct orientation atapproximately the current time in Block S122; calculating a targetdiffuse orientation of the light exposure device based on the firstlocation, the current time and date, and a diffuse solar position model,the ultraviolet sensor biased away from the Sun when the light exposuredevice occupies the target diffuse orientation at approximately thecurrent time in Block S124. Generally, Blocks S122 and S124 function tocalculate target orientations (e.g., target global, target direct, andtarget diffuse orientations) or orientation ranges based on the solarposition and at which the light exposure device can record targetedultraviolet values from the ultraviolet sensor in order to calculate anaccurate local ultraviolet index.

Block S122 of the method S100 can be implemented by the light exposuredevice to calculate a target direct orientation based on the time anddate of the current sampling interval and the current location of thelight exposure device (e.g., the location received from the mobiledevice). When the light exposure device occupies this target directorientation within the current sampling interval, the Sun is locatedwithin (or very near) the field of view of the ultraviolet sensor. Todefine the target direct orientation, the light exposure device cancalculate a solar position (i.e., a position of the Sun relative to theuser's reference frame on the Earth) based on the location of the lightexposure device and a current time and date, as described above. Thelight exposure device can then calculate an orientation of the lightexposure device at which the field of view of the ultraviolet sensorpoints directly toward the Sun. Thus, when the light exposure device isaligned with the target direct orientation, a vector normal to theultraviolet sensor may point (nearly) directly toward the center of theSun, thereby yielding a (near) maximum detectable ultraviolet value forthis sampling interval. For example, the light exposure device canpredict yaw, pitch, and roll positions (i.e., angular orientations inthree degrees of freedom relative to the light exposure device's currentreference frame) at which the ultraviolet sensor will be directed towardthe Sun during the current sampling interval given the current time,date, and location of the light exposure device and store these yaw,pitch, and roll positions as the target direct orientation for thissampling interval.

Alternatively, the light exposure device can define a range oforientations (i.e., a target direct orientation window) surrounding thetarget direct orientation such that over the range of orientations, thelight exposure device is directed toward the Sun or directed toward apoint in the sky within a threshold offset from the Sun. For example,the light exposure device can calculate a target direct orientationcorresponding with a solar position defined by a solar altitude of 38.72degrees and a solar azimuth of 263.57 degrees for the light exposuredevice location in San Francisco. Thus, the light exposure device candefine the target direct orientation along a vector oriented 38.72degrees above a horizon and 236.57 degrees from a cardinal Northdirection. Furthermore, the light exposure device can define a targetdirect orientation range encompassing an area surrounding the targetdirect orientation, a boundary of the target direct orientation rangeoffset ten degrees from the target direct orientation, effectivelydefining a conic target orientation window with an included angle oftwenty degrees.

The light exposure device can also calculate a target global orientationdirected straight upward (i.e., perpendicular a horizon) for measuringultraviolet values recorded by the ultraviolet sensor. Thus, the lightexposure device can implement Blocks of the method S100 to define thetarget global orientation, at which the ultraviolet sensor can recordultraviolet values, to be agnostic to an orientation of the Sun. Thus,ultraviolet values recorded by the light exposure device when alignedwith the target global orientation can vary as the solar positionchanges during a day.

Alternatively, the light exposure device can calculate a range oforientations (i.e., a target global orientation window) surrounding thetarget global orientation such that over the range of orientations, thelight exposure device is directed straight upward or at a slight angleto a vertical line directed straight upward toward the sky. Thus, thelight exposure device can calculate a target global orientation rangeencompassing an area surrounding the target global orientation, suchthat the light exposure device can be slightly biased away from thetarget global orientation and still record an accurate and acceptedultraviolet value.

The light exposure device can also implement Block S124 of the methodS100 to calculate a target diffuse orientation directed toward a pointin the sky biased away from the Sun. For example, the light exposuredevice can define the target diffuse orientation: that is angularlyoffset by at least 50° from the direct vector (e.g., current azimuth andzenith angle) toward the Sun to minimize an effect of low-angle directsunlight on a diffuser in the ultraviolet sensor; and angularly offsetabove horizon by at least 15° to confirm that the ultraviolet sensor isfacing the sky and not a hill or mountain. Therefore, the light exposuredevice can define a target diffuse orientation “window” or “zone”containing the whole the sky visible locally, less a sector below 15°above the horizon and less a sector ±50° from the current azimuth of theSun. The light exposure device can thus define a target diffuseorientation window: that approximates an annular zone at solar noon it;and that represents dome less a circular “keep-out” region proximal oneedge of the dome centered on the Sun.

However, the light exposure device can implement any other methods ortechniques in Blocks S122 and S124 to define discrete targetorientations or orientation windows in which the light exposure devicemay opportunistically record ultraviolet values. The light exposuredevice can repeat this process to calculate new target orientations ororientation windows for each sampling interval (e.g., once perfifteen-minute interval) based on a time and date representative of thesampling interval and based on an approximate location of the lightexposure device during the sampling interval.

5. Triggers & Ultraviolet Sampling

Blocks S142, S144, and S146 of the method S100 recite, in response todetecting alignment between orientation of the light exposure device andthe target direct orientation at approximately the current time,recording a direct ultraviolet value read from the ultraviolet sensor inBlock S142; in response to detecting alignment between orientation ofthe light exposure device and the target diffuse orientation atapproximately the current time, recording a diffuse ultraviolet valueread from the ultraviolet sensor in Block S144; in response to detectingalignment between orientation of the light exposure device and a targetglobal orientation at approximately the current time, recording a globalultraviolet value read from the ultraviolet sensor in Block S146.Generally, Blocks S142, S144, and S146 of the method S100 function tomeasure ultraviolet values when the light exposure device is alignedwith predefined target orientations or target orientation ranges. Thus,Blocks S142, S144, and S146 of the method S100 function to avoidcontinuous sampling of the ultraviolet sensor and still record acceptedultraviolet values, which can be used to calculate an ultraviolet indexand project future ultraviolet values.

4.1 Orientation Triggers

In response to detecting alignment between orientation of the lightexposure device and the target direct orientation at approximately thecurrent time (or within a sampling interval succeeding the first time),the method S100 can be implemented to record a first value read from theultraviolet sensor as a direct ultraviolet value. Generally, in BlockS142, the light exposure device can: regularly sample (e.g., at a rateof 10 Hz) orientation sensors integrated into the light exposure deviceto determine the orientation of the ultraviolet light exposure devicerelative to a reference frame; read an ultraviolet value from theultraviolet sensor when alignment between the detected orientation ofthe light exposure device falls within a tolerance of a target directorientation (or within a target direct orientation window) calculatedfor the current sampling interval in Block S122; and then store thisultraviolet value as a direct ultraviolet value (e.g., a ultravioletirradiance value in Watts per square meter) for this sampling interval.

In one variation, the light exposure device can: read a sequence ofultraviolet values from the ultraviolet sensor as the light exposuredevice sweeps through the direct orientation window, such as at a rateof 10 Hz; and then store a singular maximum ultraviolet value in thissequence of ultraviolet values as the direct ultraviolet value for thissampling interval.

Similarly, the light exposure device can: read a sequence of ultravioletvalues from the ultraviolet sensor as the light exposure device sweepsthrough the direct orientation window, such as at a rate of 10 Hz; tageach ultraviolet value in this sequence with an orientation of the lightexposure device relative to the reference frame; and then store asingular ultraviolet value in this sequence of ultraviolet values taggedwith an orientation nearest a target orientation as the directultraviolet value for this sampling interval.

Alternatively, the light exposure device can: record a first ultravioletvalue read from the ultraviolet sensor once the light exposure deviceenters an initial direct orientation window (e.g., defined by a 15° coneaxially aligned with a target direct orientation); recalculate a second,tighter direct orientation window (e.g., defined by a 10° cone axiallyaligned with a target direct orientation); replace the first ultravioletvalue with a second ultraviolet value read from the ultraviolet sensoronce the light exposure device enters the second direct orientationwindow; recalculate a third, tighter direct orientation window (e.g.,defined by a 5° cone axially aligned with a target direct orientation);replace the second ultraviolet value with a third ultraviolet value readfrom the ultraviolet sensor once the light exposure device enters thethird direct orientation window; etc. during the sampling interval,thereby refining and increasing accuracy of a direct ultraviolet valuerecorded for this sampling interval, as described below.

The light exposure device can implement similar methods and techniquesto record (and refine) a global ultraviolet value and a diffuseultraviolet value during a sampling interval.

4.2 Timing Triggers

Additionally or alternatively, the controller of the light exposuredevice can initiate and disable recording of ultraviolet valuesaccording to a schedule or timing scheme defined by and executed by thecontroller. Generally, the light exposure device can implement Blocks ofthe method S100 to avoid recording extraneous and/or irrelevantultraviolet values when ambient conditions may be adverse to recordingadvantageous ultraviolet values.

For example, the light exposure device can define (and/or access) apredicted ultraviolet value schedule, estimating ultraviolet values overtimes of the day for a current location of the light exposure device.During a night period (e.g., between sunset and sunrise), the lightexposure device can predict extremely low ultraviolet values. Thus, thelight exposure device can calculate an inactive period (e.g., the nightperiod) over which the first ultraviolet index exposure curve predictsultraviolet indices less than a threshold ultraviolet index. Thus, thelight exposure device can operate in the low-power mode during theinactive period (e.g., during the night period) and estimate anultraviolet exposure of null over the inactive period. Furthermore, thelight exposure device can reactivate the ultraviolet sensor at the endof the night period (i.e., during a day period). Similarly, undercertain date, time, and location conditions, the local ultraviolet indexmay be so low as to be insignificant, such as just after sunrise or justbefore sunset in winter; the light exposure device can thus deactivate(i.e., not sample) the ultraviolet sensor during such periods.

The light exposure device can record ultraviolet values (e.g., samplethe ultraviolet sensor) intermittently, such as every minute, everyother minute, every 15 minutes, at random, etc. Furthermore, asdescribed below, the light exposure device can alter ultraviolet sensorsampling intervals according to parameters collected by other sensors inthe light exposure device and data pulled from the mobile computingdevice.

Additionally or alternatively, the light exposure device can recordultraviolet values according to a schedule, such as a solar schedule ora personal calendar agenda of a user carrying the light exposure devicetransmitted to the light exposure device from the mobile computingdevice, in order to record ultraviolet values at times of knownultraviolet exposure. For example, the light exposure device can recordultraviolet values at solar noon as the light exposure device canpredict maximum ultraviolet exposure at solar noon.

In another example, the light exposure device can access a personalcalendar transmitted to the light exposure device from the mobilecomputing device. The light exposure device can detect a first evententitled “Hike with Katie” between 12:30 pm and 1:30 pm and a secondevent entitled “Meeting with Company A at Warehouse H” between 2:00 pmand 3:30 pm. The light exposure device can then identify that the firstevent is an outdoor event and can arm the ultraviolet sensor to recordultraviolet values (intermittently at intervals or continuously) between12:30 pm and 1:30 pm. Additionally, the light exposure device canidentify that the second event is an indoor event and can disable theultraviolet sensor between 2:00 pm and 3:30 pm. Alternatively, the lightexposure device can record ultraviolet values (and/or ambient lightvalues, as described below) intermittently (e.g., every 15 minutes)between 2:00 pm and 3:30 pm to verify ultraviolet exposure throughoutduration of the second event.

4.3 Ambient Light Triggers

As described above, the light exposure device can record ultravioletvalues measured by the ultraviolet sensor in response to alignment ofthe light exposure device with particular target orientations.Additionally or alternatively, the light exposure device can initiaterecording of ultraviolet values in response to the presence or absenceof ambient light detected by the ambient light sensor. Similarly, thelight exposure device can initiate recordation of ultraviolet values inresponse to changes in ambient light detected by the ambient lightsensor, such as may occur when the user moves from an indoor location toan outdoor location.

For example, as described above, the light exposure device can recordambient light values with an ambient light sensor integrated into thelight exposure device. At a first time, the light exposure device canrecord a first ambient light value read from the ambient light sensor.In response to detecting a first ambient light value less than a firstthreshold ambient light value, the light exposure device can identifythe ultraviolet sensor as obscured; and disable the ultraviolet sensorfrom recording ultraviolet values because, for example, if the ambientlight sensor is obscured, it is likely the ultraviolet sensor is alsoobscured. Thus, the light exposure device can initiate an inactive state(i.e., a sleep mode) for a particular duration by initiating a timer.After expiration of the timer, the light exposure device can record asecond ambient light value read from the ambient light sensor. Inresponse to detecting the second ambient light value exceeding a secondthreshold ambient light value, the light exposure device can rearm theultraviolet sensor to read ultraviolet values. However, if the secondambient light value remains below the second threshold ambient lightvalue, the light exposure device can reset the time and continue thesleep mode.

In a similar example, when recording a first value read from theultraviolet sensor as the direct ultraviolet value, the light exposuredevice can first verify presence of ambient light, record an ambientlight value detected by the ambient light sensor, and then check foralignment between a current orientation of the light exposure device anda particular target orientation (e.g., the target direct orientation).The light exposure device can also record ambient light values prior toverifying a current orientation of the light exposure device andrecording global ultraviolet values and diffuse ultraviolet values.

In a similar example, in response to detecting an ambient light valueexceeding a first threshold ambient light value at approximately thefirst time, the light exposure device can arm the controller toopportunistically record direct, diffuse, and global ultraviolet valuesduring a subsequent sampling interval. However, in response to recordingan ultraviolet value (e.g., an ultraviolet value recorded at anyorientation of the light exposure device or a direct ultraviolet valueand/or a diffuse ultraviolet value) that is less than a thresholdultraviolet value during this sampling interval, the light exposuredevice can determine that it is located indoors (e.g., inside abuilding) during the sampling interval and discard these ultravioletvalues as not representative of (significant) sun exposure. Therefore,if the light exposure device detects incident ambient light above athreshold ambient level but fails to detect incident ultraviolet lightabove a threshold ultraviolet level during a daylight period (e.g., from6 AM until 7 PM), the light exposure device can determine that it islocated indoors and discard ultraviolet values read during this samplinginterval.

Similarly, if the incident ambient light and ultraviolet levels are bothless than corresponding threshold levels during a daylight period, thelight exposure device can determine that the ambient light sensor andultraviolet sensor are obscured, such as by a shirt sleeve; the lightexposure device can discard these ultraviolet data accordingly and/orserve a prompt to the user—such as through the user's mobile computingdevice—to correct obfuscation of these sensors. However, if the incidentambient light and ultraviolet levels exceed corresponding thresholdlevels during a daylight period, the light exposure device can: confirmthat the light exposure device is located outside; and transition toopportunistically recording direct and diffuse ultraviolet values whenthe light exposure device is properly oriented during this samplinginterval. (Alternatively, the light exposure device can store theseultraviolet values directly if these ultraviolet values were recordedwhen the light exposure device was properly oriented.)

Therefore, the light exposure device can confirm its location asindoors, obscured, or outdoors based on ambient and ultraviolet datacollected for any orientation of the light exposure device or anyorientation of the light exposure device that places the ambient lightsensor and ultraviolet sensor facing upward; the light exposure devicecan then selectively execute a sampling routine to opportunisticallycollect ultraviolet data from the light exposure device when it isconfirmed to be outside. Alternatively, the light exposure device can:record an ambient light level with each ultraviolet value collectedopportunistically when the orientation of the light exposure devicematches (within a preset tolerance) a target orientation; and can mergethese ambient and ultraviolet data to confirm that the light exposuredevice was located outdoors when this ultraviolet value was recordedbefore storing this ultraviolet value in memory and implement thisultraviolet value to estimate the user's ultraviolet exposure, asdescribed below.

4.4 Location Trigger

Additionally or alternatively, the light exposure device can initiateand disable recording of ultraviolet values in response to detecting(e.g., at the mobile computing device) the light exposure device in aparticular location or detecting relocation of the light exposure devicebeyond a threshold range.

For example, the mobile computing device can detect relocation of themobile computing device from a first location to a second location at asecond time and transmit the second location and the second time to thelight exposure device. In response to detecting relocation of the mobilecomputing device from the first location to a second location greaterthan a threshold distance (e.g., one mile) from the first locationthrough sensor data (e.g., data collected by a GPS receiver at themobile computing device), the light exposure device can: calculate asecond target direct orientation of the light exposure device based onthe second location, at the second time, and the direct solar positionmodel, the ultraviolet sensor approximately normal the Sun when thelight exposure device occupies the second target direct orientation atapproximately the second time; and calculate a second target diffuseorientation of the light exposure device based on the second location,the second time, and the diffuse solar position model, the ultravioletsensor biased away from the Sun when the light exposure device occupiesthe second target diffuse orientation at approximately the second time.As described above, in response to detecting alignment betweenorientation of the light exposure device and the second target directorientation at approximately the second time, the light exposure devicecan record a fourth value read from the ultraviolet sensor as a seconddirect ultraviolet value; in response to detecting alignment betweenorientation of the light exposure device and the second target diffuseorientation at approximately the second time, the light exposure devicecan record a fifth value read from the ultraviolet sensor as a seconddiffuse ultraviolet value; and, in response to detecting alignmentbetween orientation of the light exposure device and a second targetglobal orientation at approximately the second time, the light exposuredevice can record a sixth value read from the ultraviolet sensor as asecond global ultraviolet value. From the second direct orientation, thesecond diffuse orientation, and the second global orientation, the lightexposure device can calculate a second ultraviolet index at the lightexposure device.

Alternatively, the light exposure device can implement the method S100to define its location and, based on its location, trigger ultravioletradiation sampling by the ultraviolet radiation sensor. For example, inresponse to detecting an ambient light value exceeding a first thresholdambient light value at approximately the first time, the light exposuredevice can record the first ambient light value; and, in response todetecting the direct ultraviolet value less than a threshold directultraviolet value and the diffuse ultraviolet value less than athreshold diffuse ultraviolet value at approximately the first time:locate the light exposure device in an indoor location (e.g., inside abuilding) at approximately the first time; and disable the ultravioletsensor for a period of time. At the end of the period of time, the lightexposure device can record a third ambient light value read from theambient light sensor; and, in response to detecting a third ambientlight value exceeding a third threshold ambient light value (i.e., inresponse to detecting relocation of the light exposure device to an areawhere the light exposure device is exposed to ultraviolet radiation),transitioning the ultraviolet sensor out of a low-power mode to readultraviolet values.

4.5 Weather Trigger

The light exposure device can also initiate and disable recording ofultraviolet values in response to weather data received from the mobilecomputing device.

For example, the mobile computing device can access weather data, suchas weather forecasts, Doppler radar information, etc., for the firstlocation and transmit the weather data to the light exposure device. Inresponse to receiving an indication of a change in local weather, suchas cloud-cover or precipitation proximal the first location(approximately) occupied by the light exposure device, the lightexposure device can: recalculate target diffuse and direct orientationsto target recordation of ultraviolet values when the ultraviolet sensoris facing a known atmospheric type or known surface type in the sky(e.g., open sky, a cloud); select an alternate model for associatingdirect, diffuse, and/or global ultraviolet values with a predefinedultraviolet index curve; match direct, diffuse, and/or globalultraviolet values for the current sapling interval to an ultravioletindex curve associated with a current weather condition; set a samplingrate proportional to or set a length of a sampling interval inverselyproportional to clarity of local skies, as indicated by local weatherconditions (e.g., to set a thirty-minute interval in the presence ofcloudy or overcast skies and five-minute intervals in the presence ofharsh sunlight on a clear day).

4.5 Motion

In one variation, the light exposure device can sample the orientationand ultraviolet sensors at a rate proportional to motion (e.g.,acceleration) of the light exposure device. In particular, becausegreater motion of the light exposure device may place the light exposuredevice in alignment with a target orientation or orientation window withgreater frequency, the light exposure device can sample the orientationsensors with greater frequency during such high-motion periods and thenrecord ultraviolet values through the ultraviolet sensor when the properalignment of the light exposure device is detected. Similarly, when thelight exposure device is not moving or moving only minimally, theprobability that the light exposure device will enter a targetorientation or orientation window may be relatively low; the lightexposure device can therefore not sample or sample only at a lowfrequency the orientation and ultraviolet sensors.

4.6 Tuning Orientation Windows

As described above, the light exposure device can define targetorientation windows (e.g., a target direct orientation window, a targetdiffuse orientation window, and/or a target global orientation window)over which the light exposure device remains within a threshold range ofthe target orientation. However, the light exposure device can reduce arange of the target orientation window in response to detecting aultraviolet value within the target orientation window, such that afirst offset of a boundary of the range of the target orientation windowfrom the target orientation is greater than a second offset of theultraviolet value from the target orientation. Therefore, the lightexposure device can narrow ranges over which ultraviolet values arerecorded by the ultraviolet sensor to improve accuracy and reducemeasurement error induced from discrepancies between measurementorientations and target orientations.

5. Location Change

The mobile computing device can detect relocation of the mobilecomputing device: from a first location at which the mobile computingdevice last uploaded its location to the light exposure device nearby(e.g., over short-range wireless communication protocol or a localwireless network); to a second location that is offset from the firstlocation by more than a threshold distance (e.g., twenty miles) at alater time. In this example, the mobile computing device can thentransmit the second location to the light exposure device. At a latertime, the light exposure device can then repeat Block S122 to calculatea second target direct orientation of the light exposure device based onthe approximate position of the Sun relative to the second location atthis later time, as calculated with the direct solar position model.Similarly, at this later time, the light exposure device can repeatBlock S124 to calculate a second target diffuse orientation of the lightexposure device based on the second location, this later time, and thediffuse solar position model.

The light exposure device can then opportunistically record ultravioletvalues when the light exposure device is approximately oriented in thetarget direct orientation (i.e., the ultraviolet sensor is facingapproximately directly into the Sun), when the light exposure device isapproximately oriented in the target global orientation (i.e., theultraviolet sensor is facing approximately normal to the surface of theEarth), and when the light exposure device is approximately oriented inthe target diffuse orientation (i.e., the ultraviolet sensor is facingthe sky but away from the Sun) during a concurrent sampling interval. Inparticular and as described above, in response to detecting alignmentbetween orientation of the light exposure device and the second targetdirect orientation at approximately the second time, the light exposuredevice can record a fourth value read from the ultraviolet sensor as asecond direct ultraviolet value; in response to detecting alignmentbetween orientation of the light exposure device and the second targetdiffuse orientation at approximately the second time, the light exposuredevice can record a fifth value read from the ultraviolet sensor as asecond diffuse ultraviolet value; and, in response to detectingalignment between orientation of the light exposure device and a secondtarget global orientation at approximately the second time, the lightexposure device can record a sixth value read from the ultravioletsensor as a second global ultraviolet value. From the second directorientation, the second diffuse orientation, and the second globalorientation, the light exposure device can calculate a secondultraviolet index at the light exposure device.

The light exposure device can continue to implement this second locationfor subsequent sampling intervals until an updated location is receivedfrom the mobile computing device.

5. Ultraviolet Index

Block S150 of the method S100 recites calculating a current ultravioletindex at the light exposure device based on the diffuse ultravioletvalue, the direct ultraviolet value, and the global ultraviolet value.Generally, Block S150 of the method S100 functions to calculate anultraviolet index for the current time and instant location of the lightexposure device based on the global ultraviolet index or a combination(linear or non-linear) of the diffuse ultraviolet value, the directultraviolet value, and the global ultraviolet value.

In one implementation, the light exposure device can calculate a globalultraviolet index proportional to the global ultraviolet value bycomparing the global ultraviolet value to a known mathematicalmodel—such as a ultraviolet index curve defining a regression (e.g., alinear regression) of previously recorded global ultraviolet values andultraviolet indices—that links global ultraviolet values to discreteultraviolet indices.

In another implementation, the light exposure device can calculate adiffuse ultraviolet index proportional to the diffuse ultraviolet valueby comparing the diffuse ultraviolet value to a known mathematical model(e.g., curve), defined as a regression (e.g., a linear regression) ofpreviously recorded diffuse ultraviolet values, that links diffuseultraviolet values to discrete ultraviolet indices. Similarly, the lightexposure device can calculate a direct ultraviolet index proportional tothe direct ultraviolet value by comparing the direct ultraviolet valueto a direct mathematical model, defined as a regression of previouslyrecorded direct ultraviolet values, that links direct ultraviolet valuesto discrete ultraviolet indices. Additionally, the light exposure devicecan calculate a global ultraviolet index proportional to the globalultraviolet value by comparing the global ultraviolet value to a globalmathematical model, as described above, that links global ultravioletvalues to discrete ultraviolet indices. The light exposure device canthen calculate a combination (e.g., an average) of the direct and/ordiffuse ultraviolet indices to calculate a current ultraviolet index forthe current sampling interval.

Alternatively, the light exposure device can compare the global, direct,and diffuse ultraviolet values and/or ultraviolet indices to predictwhether the user is occupying a shaded area and then selectivelytransform these ultraviolet values into a current ultraviolet index forthe current sampling interval. For example, the light exposure devicecan calculate a diffuse ultraviolet index based on (e.g., as a functionof, proportional to) the diffuse ultraviolet value and can calculate adirect ultraviolet index based on the direct ultraviolet value. Inresponse to a difference between the global ultraviolet index and thedirect ultraviolet index exceeding a threshold difference and inresponse to the global ultraviolet index remaining below the directultraviolet index, the light exposure device can: determine the lightexposure device occupied a shaded area (e.g., under a tree) at the timethat these ultraviolet values were recorded; and then determine thecurrent ultraviolet index for the current sampling interval based on thedirect and/or diffuse ultraviolet values and/or ultraviolet indices,such as by calculating an average or other combination of the diffuseultraviolet index and the direct ultraviolet index, exclusive of theglobal ultraviolet index. Similarly, if the light exposure devicecalculates global and diffuse ultraviolet indices that approximatelymatch but calculates a direct ultraviolet index that is significantlyless than the global and diffuse ultraviolet indices from global,diffuse, and direct ultraviolet values recorded during a samplinginterval, the light exposure device can determine that the lightexposure device occupied an outdoor structure (e.g., a wall, a building)that shaded the light exposure device from direct sun exposure duringthe sampling interval and thus calculate a ultraviolet index and selecta ultraviolet index curve for the sampling interval based on the globalvalue or based on the global and diffuse ultraviolet values recordedduring this sampling interval only.

Alternatively, the light exposure device can: compare the global,direct, and diffuse ultraviolet indices; identify and discard one of thethree ultraviolet indices that represents a significant outlier from theremaining to ultraviolet indices; and then average or otherwise combinethe remaining ultraviolet indices to calculate a current ultravioletindex for the current sampling interval.

However, the light exposure device can calculate a current ultravioletindex for the current sampling interval in any other way and based onany other one or combination of ultraviolet values opportunisticallyrecorded by the light exposure device during the sampling interval.

6. Redundancy & Calibration

As described above, the light exposure device can implement Blocks ofthe method S100 to calculate an ultraviolet index. By combining multipleultraviolet values recorded by the ultraviolet sensor, the lightexposure device can accurately approximate and verify the ultravioletindex regardless of an orientation or location of the light exposuredevice. Thus, through redundant recording of ultraviolet values (i.e.,the direct radiation value, the diffuse radiation value, and the globalradiation value), the light exposure device can detect and compensatefor discrepancies in ultraviolet values.

For example, the light exposure device can calculate the currentultraviolet index based on the direct ultraviolet value and calculate asecond ultraviolet index based on the diffuse ultraviolet value. Inresponse to detecting variation between the second ultraviolet index andthe current ultraviolet index greater than a threshold difference, thelight exposure device can update the current ultraviolet index based onthe second ultraviolet index, thereby correcting the current ultravioletindex with the second ultraviolet index. Furthermore, the light exposuredevice can calculate a third ultraviolet index based on the globalultraviolet value. In response to detecting variation between the thirdultraviolet index and the (updated) current ultraviolet index less thana second threshold difference, the light exposure device can thereforeconfirm the current ultraviolet index based on the third ultravioletindex. In this example, an ultraviolet index calculated from a firstultraviolet value (e.g., the diffuse ultraviolet value) can be correctedby and/or verified by additional ultraviolet indices calculated based onultraviolet values recorded in different orientations (e.g., the directand global ultraviolet values). Thus, in this implementation, the lightexposure device can implement Blocks of the method S100 to calibratesensors, such as orientation sensors, within the light exposure deviceto improve accuracy of the ultraviolet values recorded by theultraviolet sensor.

In one implementation shown in FIG. 3, the light exposure device canimplement Blocks of the method S100 to calibrate the compass sensor ofthe light exposure device. In this implementation, the compass sensorcan track an azimuth orientation of the light exposure device and thelight exposure device can define the target direct orientation and/orthe target diffuse orientation based on the azimuth orientation. Inresponse to detecting alignment between the light exposure device andthe target direct orientation, the light exposure device can record afirst direct ultraviolet value; in response to detecting alignmentbetween the light exposure device and the target diffuse orientation,the light exposure device can record a first diffuse ultraviolet value;and, in response to detecting alignment between the light exposuredevice and the target global orientation, the light exposure device canrecord a first global ultraviolet value. In response to detectingvariation among the first diffuse ultraviolet index, the first directultraviolet index, and the first global ultraviolet index exceeding thethreshold ultraviolet index, the light exposure device can define anultraviolet index curve as a combination of the first global ultravioletindex, the first diffuse ultraviolet index, and the first directultraviolet index and, similarly, define a compass calibrationcorrection curve inversely proportional to the ultraviolet index curve.Thus, the light exposure device can define the compass calibrationcorrection curve to adjust (i.e., offset) the first diffuse ultravioletindex, the first direct ultraviolet index, and the first globalultraviolet index, defined based on the azimuth orientation calculatedby the compass sensor, such that variation among the (adjusted) firstdiffuse ultraviolet index, the (adjusted) first direct ultravioletindex, and the (adjusted) first global ultraviolet index is less thanthe threshold ultraviolet index. For future calculations of the diffuseultraviolet index, the direct ultraviolet index, and the globalultraviolet index, the light exposure device can adjust (i.e., offset)the diffuse, direct, and global ultraviolet values to the compasscalibration correction curve.

Furthermore, the light exposure device can, based on discrepancies amongthe diffuse, direct, and global ultraviolet values, correct calibrationof the compass sensor (and/or other orientation sensors). In oneimplementation, in response to detecting variation among the diffuse,direct, and global ultraviolet indices exceeding the thresholdultraviolet index, the light exposure device can reject (e.g., delete orinvalidate) the target direct orientation and the target diffuseorientation as inaccurate, while maintaining the target globalorientation as a true value. From the target global orientation, thelight exposure device can calculate an expected ultraviolet index towhich the diffuse ultraviolet index and the direct ultraviolet indexcorrespond when recorded at calibrated (i.e., corrected) target diffuseand target direct orientations. Then the light exposure device cancalculate a second target direct orientation of the light exposuredevice based on the first location, the current time, the direct solarposition model, the target global orientation, and expected ultravioletvalue output by the light exposure device in the second target directorientation corresponding to the expected ultraviolet index calculatedby the light exposure device when aligned with the target globalorientation. The light exposure device can also calculate a secondtarget diffuse orientation of the light exposure device based on thefirst location, the current time, the diffuse solar position model, thetarget global orientation, and expected ultraviolet value output by thelight exposure device in the second target diffuse orientationcorresponding to the expected ultraviolet index calculated by the lightexposure device when aligned with the target global orientation. Inresponse to detecting alignment between orientation of the lightexposure device and the second target direct orientation, the lightexposure device can record a value read from the ultraviolet sensor as asecond direct ultraviolet value; and, in response to detecting alignmentbetween orientation of the light exposure device and the second targetdiffuse orientation, the light exposure device can record a value readfrom the ultraviolet sensor as a second diffuse ultraviolet value. Thus,as described above, the light exposure device can calculate a secondcurrent ultraviolet index at the light exposure device based on thesecond diffuse ultraviolet value, the second direct ultraviolet value,and the global ultraviolet value.

7. Ultraviolet Exposure

Furthermore, as shown in FIGS. 4A and 4B, Blocks S152-S156 of the methodS100 recite accessing a set of ultraviolet index curves anticipatingultraviolet indices at discrete times within a first sampling intervalsucceeding the current time based on an ultraviolet index atapproximately a first time in the first sampling interval in Block S152;at approximately the current time, selecting a first ultraviolet indexcurve from the set of ultraviolet index curves, the first ultravioletindex curve defining a first projected ultraviolet index atapproximately the current time within a threshold offset from thecurrent ultraviolet index at the current time and anticipating futureultraviolet indices for discrete times within the first samplinginterval in Block S154; and during the first sampling interval,transitioning into a low-power mode (e.g., a “sleep mode”) in BlockS156. Generally, the light exposure device can implement Block S156 tocalculate total ultraviolet exposure (i.e., exposure to ultravioletradiation quantified by an ultraviolet index) of the user over multiplediscrete sampling intervals, such as over the course of one day.Generally, an “ultraviolet index curve” can define non-parametric model,such as a lookup table. Alternatively, an “ultraviolet index curve” caninclude a parametric UV model.

In particular, the light exposure device can map recorded ultravioletvalues to predefined ultraviolet exposure models (or “curves”) to:interpolate between ultraviolet values when the ultraviolet sensorrecords ultraviolet values intermittently; and anticipate futureultraviolet indices succeeding a current time based on a lastultraviolet index recorded by the light exposure device (and/or predictpast ultraviolet indices—and therefore past ultraviolet exposurelevels—over periods of time before the light exposure device wasactively collecting ultraviolet data). For example, the light exposuredevice can access a set of ultraviolet index curves in an ultravioletexposure model. The light exposure device can then select a firstultraviolet index curve in the set of ultraviolet index curves inresponse to detecting alignment (or near alignment) between a currentultraviolet index, calculated by the light exposure device based onultraviolet values recorded at a first time, and a projected ultravioletindex, defined by the first ultraviolet index curve at the first time.Based on the first ultraviolet index curve, the light exposure devicecan anticipate future ultraviolet indices over a time period succeedingthe first time (e.g., an hour). At a second time shortly after the firsttime, the light exposure device can record a second ultraviolet valueand calculate a second ultraviolet index. However, the first ultravioletindex curve can predict an ultraviolet index at the second timesignificantly lower than the second ultraviolet index calculated by thelight exposure device. The light exposure device can implement Blocks ofthe method S100 to select a second ultraviolet index curve from the setof ultraviolet index curves in response to alignment (or near alignment)between an ultraviolet index predicted by the second ultraviolet indexcurve at the second time and the second ultraviolet index and alignment(or near alignment) between the ultraviolet index predicted by the firstultraviolet index curve at the first time and the first ultravioletindex. Thus, the method S100 can function to project future ultravioletindices and, based on projections for future ultraviolet indices,interpolate between ultraviolet radiation samples to accurately forecastintermediate ultraviolet values, thereby avoiding demand for continuoussampling of the ultraviolet sensor.

The light exposure device can also align the ultraviolet index curves to(actual) ultraviolet indices calculated by the light exposure devicefrom ultraviolet values recorded by the ultraviolet sensor.

7.1 Ultraviolet Index Curves

As shown in FIG. 4A, Block S152 of the method S100 functions to retrievea (predefined) set of ultraviolet index curves, defining ultravioletindices over a sampling interval based on an initial ultraviolet index.For a given time, each ultraviolet index curve in the set of ultravioletindex curves can define an expected ultraviolet index. For the giventime, the expected ultraviolet index of a first ultraviolet index curvein the set of ultraviolet index curves can differ from the expectedultraviolet index of a second ultraviolet index curve in the set ofultraviolet index curves. Furthermore, each ultraviolet index curve inthe set of ultraviolet index curves can predict a discrete set ofultraviolet indices over a sampling interval. For example, a firstultraviolet index curve can predict an ultraviolet index of one at afirst time, an ultraviolet index of five at a second time, and anultraviolet index of three at a third time. A second ultraviolet indexcurve can predict an ultraviolet index of 1.3 at the first time, anultraviolet index of 4.7 at the second time, and an ultraviolet index of3.4 at the third time.

In one implementation of the method S100, the light exposure device canselect a first ultraviolet index curve from the set of ultraviolet indexcurves, the first ultraviolet index curve defining a first projectedultraviolet index at approximately the current time within a thresholdoffset from the current ultraviolet index at the current time andanticipating future ultraviolet indices for discrete times within thefirst sampling interval in Block S154.

Generally, the light exposure device can select a first ultravioletindex curve that approximates the current (calculated) ultraviolet indexat the current time without a threshold margin of error. In thisimplementation, the light exposure device can, at a first time, accessthe set of ultraviolet index curves and select a first ultraviolet indexcurve from the set of ultraviolet index curves projecting an ultravioletindex at the first time nearest the current ultraviolet index calculatedand recorded by the light exposure device. Thus, the first ultravioletindex curve can predict ultraviolet indices over a sampling intervalsucceeding the first time.

Alternatively, the device can select a first ultraviolet index curvethat approximates the current (calculated) ultraviolet index at thecurrent time without a threshold margin of error and then subsequentlyadjust the first ultraviolet index curve to fit (i.e., align with) thecurrent calculated ultraviolet index at the first time. Generally, inthis implementation, the method S100 can function to compensate forvariations in total ozone (e.g., ozone levels, cloud cover, carbondioxide levels, etc.) that affect magnitude of ultraviolet radiationrecorded by the light exposure device.

7.2 Ultraviolet Exposure

Additionally, the light exposure device can apply the ultraviolet indexcurves to track total exposure over a sampling interval while avoidingcontinuous sampling of the ultraviolet sensor. Generally, the lightexposure device can calculate an ultraviolet exposure over a samplinginterval by integrating a (net) ultraviolet index exposure curve overthe sampling interval.

In one implementation shown in FIG. 4B, the light exposure device canrecord ultraviolet values intermittently over a sampling interval andcalculate ultraviolet indices corresponding to the (intermittentlyrecorded) ultraviolet values over the sampling interval in response totriggers, as described above. Thus, as described above, the lightexposure device can select a first ultraviolet index curve correspondingto (or approximating) a first ultraviolet index value calculated by thelight exposure device at a first time. From the ultraviolet index curve,the light exposure device can predict ultraviolet indices at timessucceeding the first time. However, at a second time succeeding thefirst time, the light exposure device can be triggered to record asecond direct ultraviolet value, a second diffuse ultraviolet value, anda second global ultraviolet value. From the second direct, diffuse, andglobal ultraviolet values, the light exposure device can calculate asecond ultraviolet index for the second time. However, the firstultraviolet index curve can predict a third ultraviolet index distinctfrom (e.g., less than or greater than) the second ultraviolet index atthe second time. Thus, the light exposure device can select a secondultraviolet index curve predicting an ultraviolet index value at thesecond time corresponding to (or approximating) the second ultravioletindex at the second time. Furthermore, for times succeeding the secondtime within the sampling interval, the light exposure device can applythe second ultraviolet index curve instead of the first ultravioletindex curve to predict future ultraviolet indices over the samplinginterval. Thus, to track cumulative ultraviolet exposure from the firsttime to a third time succeeding the second time, the light exposuredevice can define a cumulative ultraviolet index exposure curve bycombining the first curve and the second curve—the second curve defininga step-wise jump in the ultraviolet index at the second time. Byintegrating the cumulative index exposure curve over the samplinginterval between the first time and the third time, the light exposuredevice can calculate a cumulative ultraviolet exposure over the samplinginterval.

However, the light exposure device can track and integrate ultravioletexposure in any other way suitable to determine overall ultravioletexposure.

7.3 Ultraviolet Index Curve Adjustment

Additionally or alternatively, the light exposure device can implementBlocks of the method S100 to adjust the ultraviolet index curves toalign with ultraviolet indices calculated from ultraviolet valuesrecorded by the light exposure device.

For example, as described above, the light exposure device can select anoriginal ultraviolet index curve approximating a current ultravioletindex calculated by the light exposure device based on the direct,diffuse, and/or global ultraviolet values recorded by the ultravioletsensor at a first time and anticipating future ultraviolet indices for asampling interval succeeding the first time, assuming clear sky, outdoorambient conditions surrounding the light exposure device (e.g., a totalozone factor of zero). However, the ultraviolet index curve can predicta projected ultraviolet index at the first time less than (or greaterthan) the current ultraviolet index. Thus, the light exposure device canadjust the ultraviolet index curve to align with the current ultravioletindex, thereby defining an alignment offset between the (original)projected ultraviolet index and the current ultraviolet index.Furthermore, the light exposure device can adjust the ultraviolet indexcurve to anticipate future ultraviolet indices, adjusting the (original)ultraviolet index curve in its entirety by the alignment offset. Fromthe alignment offset, the light exposure device can determine a totalozone factor that accounts for discrepancies between the originalultraviolet index curve and an adjusted ultraviolet index curve andcompensate for variations in ambient conditions, such as cloud cover,high ozone values, time in a shaded area, etc.

However, the light exposure device can compensate for deviation betweenrecorded and predicted ultraviolet indices in any other way in order toyield accurate ultraviolet exposure metrics with intermittentultraviolet radiation measurements.

8 Notifications

One variation of the method S100 includes, in response to detecting thetotal ultraviolet exposure exceeding a threshold exposure, transmittinga notification or alert to the mobile computing device indicatingprojection of excess ultraviolet exposure over the first samplinginterval and the third sampling interval. Generally, this variation ofthe method S100 functions to notify a user carrying a light exposuredevice of excessive ultraviolet exposure, which may increase the user'srisk for erythema, skin damage, heat stroke, etc.

For example, the light exposure device can calculate an aggregateultraviolet exposure over a time period, such as four hours. In responseto the aggregate ultraviolet exposure exceeding a predefined threshold,the light exposure device can predict when a user associated with thelight exposure device will experience skin damage and publish acountdown timer to the mobile computing device to notify the user of aduration until such skin damage will occur. Furthermore, the lightexposure device can issue intermittent alerts for the mobile computingdevice to render, such as on a display, to remind a user to reapplysunscreen, head indoors during a peak exposure sampling interval, put ona hat or visor, etc.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

I claim:
 1. A method comprising: tracking an orientation of a mobiledevice comprising an ultraviolet sensor configured to detect intensityof incident ultraviolet radiation; in response to the orientation of themobile device falling within a target global orientation window at afirst time, storing a first value read from the ultraviolet sensor atapproximately the first time as a first global ultraviolet value; andcalculating a first ultraviolet index proximal a first location of themobile device at the first time based on the first global ultravioletvalue.
 2. The method of claim 1, further comprising: accessing a set ofultraviolet index curves, each ultraviolet index curve defining a seriesof ultraviolet indices as a function of time; selecting a firstultraviolet index curve, from the set of ultraviolet index curves,defining a first predicted index value approximating the firstultraviolet index, for the first time; and estimating a firstultraviolet exposure at the mobile device by integrating the firstultraviolet index exposure curve from the first time to a second timesucceeding the first time.
 3. The method of claim 2, further comprising:in response to recording the first global ultraviolet value,transitioning into a low-power mode for a preset duration of time at themobile device; in response to conclusion of the preset duration of time:entering a high-power mode at the mobile device; tracking theorientation of the mobile device; in response to the orientation of themobile device falling within the target global orientation window at thesecond time, storing a second value read from the ultraviolet sensor atapproximately the second time as a second global ultraviolet value; andcalculating a second ultraviolet index proximal a second location of themobile device at the second time based on the second global ultravioletvalue; and selecting a second ultraviolet index curve, from the set ofultraviolet index curves, defining a second predicted index valueapproximating the second ultraviolet index for the second time; andestimating a second ultraviolet exposure at the mobile device byintegrating the second ultraviolet index exposure curve from the secondtime to a third time succeeding the second time.
 4. The method of claim3, further comprising: calculating a total ultraviolet exposure based ona sum of the first ultraviolet exposure and the second ultravioletexposure; in response to the total ultraviolet exposure exceeding athreshold ultraviolet exposure, serving a prompt to a user associatedwith the mobile device to reduce sun exposure.
 5. The method of claim 4,wherein serving the prompt to the user comprises rendering anotification, to apply sunscreen, via a display integrated into themobile device.
 6. The method of claim 4, wherein serving the prompt tothe user comprises wirelessly transmitting a notification, to seekshade, from the mobile device to an external handheld device associatedwith the user.
 7. The method of claim 1: wherein storing the first valueread from the ultraviolet sensor at approximately the first time as thefirst global ultraviolet value comprises, in response to the orientationof the mobile device falling within a first threshold angular range of avertical orientation at the first time: sampling the first value fromthe ultraviolet sensor at approximately the first time; and storing thefirst value as the first global ultraviolet value; and furthercomprising: in response to the orientation of the mobile device fallingwithin a second threshold angular range of the vertical orientation at asecond time succeeding the first time, the second threshold angularrange less than the first threshold angular range, sampling a secondvalue from the ultraviolet sensor at approximately the second time; inresponse to the second value exceeding the first value, overwriting thesecond value to the first global ultraviolet value.
 8. The method ofclaim 1, further comprising: accessing the first location of the mobiledevice at the first time; calculating a target direct orientation windowin which the ultraviolet sensor falls within a threshold angular rangeof normal to the Sun at approximately the first time based on the firstlocation; in response to the orientation of the mobile device fallingwithin the target direct orientation window during a second time,storing a second ultraviolet value read from the ultraviolet sensor atapproximately the second time as a first direct ultraviolet value, thefirst time and the second time occurring within a first time interval;calculating a direct ultraviolet index based on the direct ultravioletvalue; and in response to variation between the global ultraviolet indexand the direct ultraviolet index exceeding a threshold difference and inresponse to the direct ultraviolet index remaining below the globalultraviolet index, determining that the mobile device is occupying ashaded area during the first time interval.
 9. The method of claim 8,further comprising: calculating a target diffuse orientation window inwhich the ultraviolet sensor is biased away from the Sun atapproximately the first time based on the first location; in response tothe orientation of the mobile device falling within the target diffuseorientation window during a third time within the first time interval,storing a third ultraviolet value read from the ultraviolet sensor atapproximately the third time as a first diffuse ultraviolet value;calculating a diffuse ultraviolet index based on the diffuse ultravioletvalue; and in response to determining that the mobile device isoccupying a shaded area during the first time interval, estimating afirst ultraviolet exposure at the mobile device during the first timeinterval based on the diffuse ultraviolet index.
 10. The method of claim8, wherein storing the second ultraviolet value read from theultraviolet sensor at approximately the second time as the first directultraviolet value comprises: during the time interval, recording asequence of ultraviolet values read from the ultraviolet sensor whilethe orientation of the mobile device falls within the target directorientation window; selecting the second ultraviolet value, from thesequence of ultraviolet values, greater than each other ultravioletvalue in the sequence of ultraviolet values; and storing the secondultraviolet value as the first direct ultraviolet value.
 11. The methodof claim 1: further comprising: accessing the first location of themobile device at the first time; calculating a target direct orientationwindow in which the ultraviolet sensor falls within a threshold angularrange of normal to the Sun at approximately the first time based on thefirst location; in response to the orientation of the mobile devicefalling within the target direct orientation window during a secondtime, storing a second ultraviolet value read from the ultravioletsensor at approximately the second time, the first time and the secondtime occurring within a first time interval; estimating an angularoffset from a primary axis of the ultraviolet sensor to the Sun when thesecond ultraviolet value was recorded; and calculating a first directultraviolet value proximal the mobile device during the first intervalbased on the second ultraviolet value, corrected based on the angularoffset; and wherein calculating the first ultraviolet index comprisescalculating the first ultraviolet index proximal the first location ofthe mobile device at the first time based on the first globalultraviolet value and the first direct ultraviolet value.
 12. A methodcomprising, during a first sampling interval: accessing a first locationof a mobile device comprising an ultraviolet sensor configured to detectintensity of incident ultraviolet radiation; based on the first locationand a time and a date of the first sampling interval, calculating atarget direct orientation of the mobile device for which a primary axisof the ultraviolet sensor is approximately normal to the Sun during thefirst sampling period; tracking an orientation of the mobile device; inresponse to the orientation of the mobile device approximately aligningwith the target direct orientation at a first time, storing a firstvalue read from the ultraviolet sensor at approximately the first timeas a first direct ultraviolet value; and calculating a first ultravioletindex proximal a first location of the mobile device at the first timebased on the first direct ultraviolet value.
 13. The method of claim 12,further comprising: accessing a generic ultraviolet index curve defininga series of ultraviolet indices as a function of time; adjusting thegeneric ultraviolet index curve to approximate the first ultravioletindex for the first time; and estimating a first ultraviolet exposure atthe mobile device by integrating the generic ultraviolet index exposurecurve, adjusted according to the first ultraviolet index, from the firsttime to a second time succeeding the first time.
 14. The method of claim13, further comprising: in response to recording the first directultraviolet value, transitioning into a low-power mode for a presetduration of time at the mobile device; in response to conclusion of thepreset duration of time: entering a high-power mode at the mobiledevice; tracking the orientation of the mobile device; in response tothe orientation of the mobile device approximately aligning with thetarget direct orientation at a second time, storing a second value readfrom the ultraviolet sensor at approximately the second time as a seconddirect ultraviolet value; and calculating a second ultraviolet indexproximal a second location of the mobile device at the second time basedon the second direct ultraviolet value; and adjusting the genericultraviolet index curve to approximate the second ultraviolet index forthe second time; and estimating a second ultraviolet exposure at themobile device by integrating the generic ultraviolet index exposurecurve, adjusted according to the second ultraviolet index, from thesecond time to a third time succeeding the second time; calculating atotal ultraviolet exposure based on a sum of the first ultravioletexposure and the second ultraviolet exposure; and in response to thetotal ultraviolet exposure exceeding a threshold ultraviolet exposure,serving a prompt to a user associated with the mobile device to reducesun exposure.
 15. A method for measuring visible ultraviolet lightradiation comprising: accessing a first location of a mobile devicecomprising an ultraviolet sensor configured to detect intensity ofincident ultraviolet radiation; tracking an orientation of the mobiledevice; during a first sampling interval: in response to the orientationof the mobile device approximately aligning with a target directorientation facing the Sun at a first time, recording a firstultraviolet value read from the ultraviolet sensor at approximately thefirst time as a direct ultraviolet value; in response to the orientationof the mobile device approximately falling within a target diffuseorientation window biased away from the Sun at a second time, recordinga second ultraviolet value read from the ultraviolet sensor atapproximately the second time as a diffuse ultraviolet value; inresponse to the orientation of the mobile device approximately aligningwith a target global orientation facing vertically upward at a thirdtime, recording a third ultraviolet value read from the ultravioletsensor at approximately the third time as a global ultraviolet value;and calculating a first ultraviolet index proximal the mobile device atthe first location during the first sampling interval based on acombination of the direct ultraviolet value, the diffuse ultravioletvalue, and the global ultraviolet value.
 16. The method of claim 15:further comprising: calculating a diffuse ultraviolet index as afunction of the diffuse ultraviolet value; calculating a directultraviolet index proportional to the direct ultraviolet value;calculating a global ultraviolet index proportional to the first globalultraviolet value; and in response to variation between the diffuseultraviolet index, the direct ultraviolet index, and the globalultraviolet index falling below a threshold difference, predictingdirect sunlight at the first location; and in response to variationbetween the diffuse ultraviolet index, the direct ultraviolet index, andthe global ultraviolet index exceeding the threshold difference,predicting indirect sunlight at the first location; and whereincalculating the first ultraviolet index comprises: in response topredicting direct sunlight at the first location, calculating the firstultraviolet index based on the combination of the direct ultravioletvalue, the diffuse ultraviolet value, and the global ultraviolet value;and in response to predicting direct sunlight at the first location,calculating the first ultraviolet index based on the global ultravioletvalue.
 17. The method of claim 15, further comprising: calculating adiffuse ultraviolet index as a function of the diffuse ultravioletvalue; calculating a direct ultraviolet index proportional to the directultraviolet value; and in response to variation between the globalultraviolet index and the direct ultraviolet index exceeding a thresholddifference and the global ultraviolet index remaining below the directultraviolet index: determining that the mobile device is occupying ashaded area; and calculating the current ultraviolet index based on thediffuse ultraviolet index and the direct ultraviolet index.
 18. Themethod of claim 15: further comprising: based on the first location anda time and a date of the first sampling interval, calculating the targetdirect orientation of the mobile device for which a primary axis of theultraviolet sensor is approximately normal to the Sun during the firstsampling period; defining a target direct orientation window around thetarget direct orientation; and defining the target diffuse orientationwindow disjoint from the target direct orientation window; and whereinrecording the first ultraviolet value as the direct ultraviolet valuecomprises, in response to the orientation of the mobile device fallingwithin the target direct orientation window at the first time: readingthe first ultraviolet value from the ultraviolet sensor; and storing thefirst ultraviolet value as the direct ultraviolet value.
 19. The methodof claim 15: further comprising: calculating a first vector, within areference frame, parallel to gravity detected by the mobile device;defining the target global orientation along the first vector: defininga target global orientation window in the form of a first cone coaxialthe first vector; identifying a solar zenith of the Sun relative to afirst location of the mobile device at a current time and date; defininga second vector, within the reference frame, directed toward a center ofthe Sun based on the solar zenith; and defining the target directorientation along the second vector: defining a target directorientation window in the form of a second cone coaxial the secondvector; and defining the target diffuse orientation window, within thereference frame, comprising a three-dimensional zone extending above thehorizon, excluding a first sector below a threshold angle above thehorizon, and excluding a second sector comprising the solar zenith ofthe Sun at the current time and date; wherein recording the firstultraviolet value as the direct ultraviolet value comprises, in responseto the orientation of the mobile device falling within the target directorientation window at the first time: reading the first ultravioletvalue from the ultraviolet sensor; and storing the first ultravioletvalue as the direct ultraviolet value; and wherein recording the thirdultraviolet value as the global ultraviolet value comprises, in responseto the orientation of the mobile device falling within the target globalorientation window at the first time: reading the third ultravioletvalue from the ultraviolet sensor; and storing the third ultravioletvalue as the global ultraviolet value.
 20. The method of claim 15:further comprising: during an initial sampling interval preceding thefirst sampling interval: reading an initial visible light value from avisible light sensor integrated into the mobile device; reading aninitial ultraviolet value from the ultraviolet sensor; in response tothe initial visible light value exceeding a threshold visible lightlevel and in response to the initial ultraviolet value falling below athreshold ultraviolet level: predicting indoor occupancy of the mobiledevice; transitioning into a low-power mode for a preset duration oftime at the mobile device; and estimating a null ultraviolet indexproximal the mobile device during the initial sampling interval; furthercomprising, in response to conclusion of the preset duration of time:entering a high-power mode at the mobile device during the firstsampling interval; reading a first visible light value from the visiblelight sensor; reading a fourth initial ultraviolet value from theultraviolet sensor; and in response to the fourth ultraviolet valueexceeding the threshold ultraviolet level, predicting outdoor occupancyof the mobile device; and wherein tracking the orientation of the mobiledevice and calculating the first ultraviolet index proximal the mobiledevice comprises, in response to predicting outdoor occupancy of themobile device, tracking the orientation of the mobile device andcalculating the first non-zero ultraviolet index proximal the mobiledevice.
 21. The method of claim 15, wherein calculating the firstultraviolet index comprises calculating one of UVA irradiance index, UVBirradiance index, and erythemal UV irradiance index proximal the mobiledevice at the first location during the first sampling interval based onthe combination of the direct ultraviolet value, the diffuse ultravioletvalue, and the global ultraviolet value.